Given: f : Z → Z
(a) f(x) = x3
It is one-one but not onto.
Thus, it is not bijective.
(b) f(x) = x + 2
It is one-one and onto.
Thus, it is bijective.
(c) f(x) = 2x + 1
It is one-one but not onto.
Thus, it is not bijective.
(d) f(x) = x2 + 1
It is neither one-one nor onto.
Thus, it is not bijective.
Hence, the correct option is (b).